In flat panel displays, such as the flat panel projection TV system, a transparent substrate, such as quartz or glass plates have been used to fabricate TFT active matrices. The area occupied by the TFT, a storage capacitor, and a metal conductor of the pixel significantly reduces the transmission ratio of the display. In addition light losses are caused by absorption of the substrate, indium tin oxide (ITO) electrodes and the liquid crystal material itself.
In the reflective mode of a LCD panel, there is a great flexibility of matrix array layout for pixels without any restriction on type of substrate. The major problem that occurs in manufacturing such displays is planarization of the substrate to form a good reflective surface.
An example of such planarization in a reflective LCD panel may be seen in Japanese Reference No. 55-32026(A) in which a field effect transistor (FET) is formed on a silicon substrate and covered with flattening layers of a varnish-type insulation. This flattening layer prevents serration where vapor deposition films do not deposit during the subsequent formation of transparent conductive film layers and orientation films for the liquid crystal.
Also in U.S. Pat. No. 4,205,425, a planar liquid crystal matrix array structure is made by using a smoothing layer of appropriate materials. Such smoothing material is identified as a polyimide and subsequent reflective electrodes are formed thereover.
A major concern in constructing reflective LCD panels involves the elimination of leakage currents in the TFT induced by light entering the structure between reflective electrodes of the pixel areas. The present invention obviates this problem by constructing a SOI type of transistor beneath the reflective electrode in such a manner that leakage currents from the transistor are prevented.